A dental ceramic can be coloured or opacified e.g. by incorporating pigments into the ceramic material from the very beginning or using metal salts containing solutions which are applied on the surface of a porous dental ceramic article with the aim to colour the dental ceramic article in its entirety. Colouring solutions are described in a couple of documents:
WO 00/46168 (corresponding to U.S. Pat. No. 6,709,694) refers to colouring ceramics by way of ionic or complex-containing solutions containing defined concentrations of at least one salts or complexes of the rare earth elements or of the elements of the subgroups. The solution might contain additives like stabilizers, complex builders, pigments and beating additives.
WO 2004/110959 (3M IPC) relates to a colouring solution for ceramic framework. The solution comprises a solvent (e.g. water), a metal salt and polyethylene glycol having a Mn in the range of 1.000 to 200.000.
WO 2008/098157 (3M IPC) relates to a colouring solution for dental ceramic framework comprising a solvent, a colouring agent comprising metal ions, and a complexing agent, wherein the amount of complexing agent is sufficient to dissolve the colouring agent in the solvent.
WO 2009/014903 (3M IPC) relates to a colouring solution for dental ceramic articles, the solution comprising a solvent and a colouring agent comprising rare earth element ions being present in the solution in an amount of at least 0.05 mol/l solvent and transition ions being present in the solution in an amount of 0.00001 to 0.05 mol/l solvent.
WO 2013/055432 (3M IPC) relates to aerogels, calcined and crystalline articles and methods of making the same are described. The content of this application is herewith incorporated by reference.
WO 2013/022612 (3M IPC) relates to colouring solutions for selectively treating the surface of dental ceramic articles. The solution comprises a solvent being miscible with water but not being water, an effect agent and a complexing agent.
Whitening agents are typically used to cover the metallic surface of a metallic dental framework in order to give the final dental restoration a more natural appearance. In certain cases, it can, however, also be desirable to opacify e.g. the inner surface of a ceramic framework to cover discolourations of the tooth stump.
In this respect WO 2013/070451 (3M IPC) describes a process for selectively treating parts of the surface of a porous dental ceramic using a composition comprising a liquid being miscible with water, but not being water, a whitening agent comprising nano-sized metal oxide particles, metal ion containing components or mixtures thereof which precipitate if the composition is adjusted to a pH above 5.
The present invention is intended to improve the known colouring and/or whitening processes.